How do defects influence spinodal decomposition?

Check out work from Xuyang Zhou, Gregory Thompson, and their colleagues at the University of Alabama, the Max-Planck Institut für Eisenforschung, the Federal Institute for Materials Research and Testing (BAM), and Sandia National Laboratories, using the Hummingbird Scientific tomography sample holder to characterize the influence of diverse grain boundaries on spinodal decomposition. The team combines precession electron diffraction (PED) with atom-probe tomography (APT) and density-based phase-field modeling (DPF) to investigate the temporal evolution of chemical decomposition near grain boundaries of a Pt-Au nanocrystalline system.

a) PED orientation and GB map for the annealed Pt-11Au film. b) The extracted GB map constructed to a density map, used to build the 3D simulation box. c) Atom map reconstruction with 0.15 atomic fraction Au iso-concentration surface embedded and matching grain boundary Au concentration map. d) 3D DPF simulation results of the temporal evolution of solute redistributions (12 sub-figures). Copyright © 2021 Acta Materialia Published by Elsevier Ltd. All rights reserved.

The cross-compatibility of the Hummingbird Scientific holder tip allowed PED and APT to be performed on the same sample in one workflow. Grain boundaries of different character were found to exhibit unique miscibility gaps profoundly altering the critical concentrations to initiate during spinodal decomposition, which then alters the decomposition pathway. The grain boundaries pull solutes from the bulk, driving a stable single-phase the bulk interior. Near grain boundaries, especially high-angle grain boundaries (HAGB), the solute threshold for spinodal decomposition is raised. The work suggests that a high fraction of HAGBs may stabilize a more homogenous segregation network  for nanocrystalline alloy design.

Reference: Xuyang Zhou, Reza Darvishi Kamachali, Brad L. Boyce, Blythe G. Clark, Dierk Raabe, Gregory B. Thompson, Acta Materialia 215  117054 (2021) DOI: 10.1016/j.actamat.2021.117054

Full paper Copyright © 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

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